1. Field of the Invention
This invention relates to security alarm systems, and more particularly, to a fire and burglary detection system for providing alarm indications in response to the detection of a fire in a building or an unauthorized entry of the building.
2. Description of the Prior Art
Numerous security alarm systems have been proposed for detecting conditions such as fire or unauthorized entry of a building protected by the system and for providing suitable alarms in the event of detection of such conditions. Such systems generally include a plurality of sensing devices which are operable to detect conditions such as fire, smoke, unauthorized entry, etc. of a building protected by the system, and to provide suitable indications of the detection of such conditions to a common receiver which effects the generation of an audible alarm, for example, to alert occupants of the building to the condition detected.
Heretofore two types of security systems have been employed: (a) wired systems in which the sensors are connected directly to a control panel, and (b) wireless systems in which the sensors control suitable transmitter units to generate high frequency signals, generally in the RF band, for transmission to a receiver which is connected to a control panel.
When a large number of sensors are employed, a wired system becomes impractical both from the cost standpoint and the need for extending wires from the sensors to the receiver. The problem becomes more evident when one considers the increased capabilities of systems presently available. That is, not only do such systems provide for the detection of fire at locations throughout the building, the protection for numerous doors and windows, or guarding against an intruder who manages to avoid detection upon entering the building through the use of further sensors within the building, but also such systems may incorporate provisions for manually operated alarms, authorized entries, exit delays and other features. Moreover, the desirability of providing distinct alarm indications in response to the detection of different alarm conditions further complicates the layout and installation of the systems. Wireless systems are generally less expensive than wired systems. However, wireless systems are characterized by various interference problems, particularly those systems adapted for residential application. Such systems, which employ RF signalling to enable transmission of alarm indications from the transmitter units to the receiver, are susceptible to interference from RF signals generated by citizens band transmitters or from a similar security alarm system which protects a neighboring house. Likewise, RF alarm signals generated by transmitters of a system which protects a given house may also provide interference with a similar system employed in an adjacent house.
It is pointed out, the transmitter units of wireless systems are generally battery powered since it would be impractical to turn on each of the many transmitters located throughout the building whenever it is desired to activate the system. Accordingly, the receiver is generally turned off at times when the protection is not needed. Thus, even though a transmitter unit controlled by an entry switch for a protected door will provide an RF alarm signal whenever the door is opened, such signal will not cause an audible alarm to be provided when the receiver is deactivated.
However, where neighboring houses each employ RF security alarm systems, then should one system be activated while the occupants of the house protected by such system are away, the RF alarm signals generated by alarm transmitters which protect a neighboring house, as may be provided in response to opening a protected door or window while the receiver of such system is deactivated, may trigger a false alarm in the neighboring system. The alarm would result in the provision of an audible alarm and may also be transmitted to the police department or some other security watch service.
This interference problem can be minimized by making the transmitters and receivers adjustable to a number of frequencies. However, when two systems interfere with each other and adjustment of the transmitting frequencies is required after a system has been installed, a problem may arise in making a determination as to who will pay for such adjustments.
A further consideration is the installation requirements for the transmitter units. Various types of sensing devices, including heat detectors, entry switches, manual push-buttons and the like may be employed by a given system.
Thus, different applications will have different mounting and packaging requirements. For example, transmitter units associated with entry switches must be mounted near the doors and windows they protect.
With the large number of sensors to be mounted, it would be desirable to have universal alarm transmitter units which accommodate different types of alarm sensors and which are of small size and easy to install.
It would also be desirable to have a security alarm system for a building which minimizes the effects of interference from extraneous RF signals in the proximity of the building.
It would be further desirable to have a security alarm system employing battery operated transmitter units in which drain on the batteries is minimized.